Streetlight reform I

[Peter B. Hansen]

Glare?  Why you should care!

by

Gary Green

Glare.  Even the word sounds annoying.  As annoying as that icy stare from your aunt at Thanksgiving.  But the glare that we’re talking about here is caused by poor lighting.  It’s the light that enters your eye directly from a light source, such as a headlight or an unshielded bulb.  It’s annoying and, at times, can be dangerous because it can actually hide things from our sight.

OK, you may ask, how can light hide things from my sight?  Doesn’t it illuminate what I can’t otherwise see?  Well, sometimes yes, but frequently not.  Light is usually intended to brighten up a place so that people can find their way, can see if anyone else is in the vicinity, or to make sure that someone else isn’t.  We have been taught that light is used for our safety, comfort and well-being and, if it is used effectively or efficiently, it can do that intended job.  The problem is that most of us haven’t learned a few simple principles of good lighting and, all to often, take the quickest, cheapest or easiest way to solve many lighting issues.  Unfortunately, many of us might mistakenly agree that, as far as light is concerned, more is better!

However, the indiscriminate use of light, especially light that is not well shielded, sometimes makes for poorer visibility because of glare.

Glare is caused by light entering your eye directly from a light source.  With unshielded lights, your eye may see the filament (the source), or either a reflection or refraction of it.  Reflection may involve the filament light reflecting off a mirror; refraction may be a lens that collects the light and broadcasts it to the surroundings, like the “bug eye” lenses on most of the streetlights in Acton.  The source is the brightest part of any light and your eye acts in a very predictable and characteristic way whenever it sees too much light – it starts to shut down.

Your eye evolved to automatically reduce the size of your iris when high levels of light enter your eye.  Also, the rods and cones of your retina (the parts that detect color and intensity) are interconnected, so that when a bright spot of light is focused on one part of the retina, the rods and cones around this spot instantly reduce their sensitivity. This is nature’s way of preventing you from being blinded, but it comes with a penalty - your eyes become less sensitive to light from all other parts of the scene you are observing.  Both the intensity and contrast of everything in the scene is reduced because of one bright spot.  As an example of this effect, remember the last time you went outdoors at night and allowed your eyes to “dark adapt” for a while.  You could see fainter and fainter stars and more details in the surrounding shrubbery as time went on.  Now imagine if your neighbor suddenly turned on his outside floodlight in your direction.  Your eyes would react immediately and you no longer would be able to see the stars, or the shrubbery and maybe not even your neighbor’s house.  The glare from the light effectively obscures all the low light details you could see before.

Glare caused by inappropriate lighting therefore can greatly diminish our ability to see things at night.  Because glare causes our eyes to react this way, two relatively simple and cheap solutions to minimize it are to re-aim lights and to shield the source of the lights from direct observation.  Streetlights, floodlights and even those simple incandescent bulbs on your outside lamppost can be re-aimed or shielded to reduce the effect of glare on passers-by.  Good shielding is something that can and should be addressed by town municipalities, businesses and individual citizens.  The result can be safer and better use of the redirected light for its intended purposes.

We may not be able to eliminate all sources of glare at night – and probably not that annoying glare from your aunt – but we can all make a difference in our surroundings with a little effort.